Improved Load Rating of Reinforced-Concrete Box Culverts Using Depth-Calibrated Live-Load Attenuation

Abstract

This paper describes depth-calibrated live-load attenuation for the load rating of reinforced-concrete box culverts using production-simplified models. In-plane depth calibration is accomplished using a production-simplified, two-dimensional, linear-elastic, finite-element, soil-structure interaction model with results compared with those from the recommended direct-stiffness, structural-frame model. Out-of-plane live-load attenuation considers each potential critical section depth rather than the cover soil depth only. The effectiveness of depth calibration is assessed by comparing predicted live-load moments obtained from the models versus measured live-load moments obtained from full-scale culvert load tests. A load rating case study illustrates the potential for improved alignment between load rating and observed performance. Findings show that depth calibration improves current load rating practice by increasing the accuracy and precision of live-load demand predictions, particularly in culvert walls and bottom slabs. Use of the depth-calibrated soil-structure model helps close the disconnect between calculated load rating and observed structural performance by more accurately predicting both the location of the weakest critical section and the live-load magnitude. The depth-calibrated soil-structure model also moves the predicted live load toward more uniform accuracy and precision across all sections.